Simulation roof pond and thermal mass effect of it

I tried to simulate the effect of a roof pond of a tiny house. At first, I can’t find any liquid material for simulation in the honeybee. So I just created a custom material to only apply some parameters of water on it.

I don’t think it is the right way. Then I use honeybee add internal mass to the same surface of one zone’s roof to make it as a thermal mass material.

I want to test the thermal mass effect of the roof pond in one house but in different zones. Then I made another house to test the performance without a roof pond as a comparison.

Questions: 1. I don’t think my method of applying materials as water’s property is a correct way to test liquid material performance.
2. The result shows that the house with thermal mass roof got even worse PMV and no difference in interior temperature. It must be somewhere wrong with my input.

3. What is the key output that I should concern for the effect of the thermal mass? Is interior air temperature or MRT or cooling load?
4. Can anyone tell me how to get the effect of thermal mass and figure out how much temperatures does it reduce for interior comparing with the building without thermal mass?
Any help is appreciated! Thank you!
roof pond thermal mass (1.0 MB)